1. Field of the Invention
The present invention relates to drum type washing machines. More particularly, the present invention relates to balance weights for drum type washing machines that reduce vibration caused by laundry imbalance.
2. Discussion of the Related Art
Generally, a washing machine removes laundry dirt and stains using chemical decomposition and mechanical impact. Modem washing machines are usually one of two basic types, a drum type and a pulsator type. The drum type washing machine is usually more compact than the pulsator type washing machine, has a greater washing capacity, and has reduced laundry entanglements. Thus, demand for drum type washing machines is increasing.
The construction of a typical drum type washing machine is explained briefly by referring to FIG. 1. As shown, a drum type washing machine includes a tub 2 that is supported by a damper 7 and by a spring 6, which are both attached to a body 1. A rotating cylindrical drum 3 is installed in the tub 2. A driving part 5 is coupled to the drum 3 by a shaft 4. The driving part 5, which is installed at the rear of the tub 3, includes a rotor 5b and a stator 5a. The shaft 4 rotates with the drum 3 and is beneficially directly coupled to the rotor 5b to transfer driving force directly to the drum 3 without that aid of a pulley or belt.
Still referring to FIG. 1, a door 8 is installed at the front of the body 1. A gasket 9 is installed between the door and drum to maintain the drum 3 airtight. A controller part 10 is installed over the door 8 to enable an operator to control the operation of the washing machine. Additionally, balance weights 14 and 15 are installed on the tub 2 to prevent vibration of the driving part 5 when laundry in the drum 3 is imbalanced.
The washing machine operates when the turning force of the rotor 5b is transferred to the drum 3 through the washing shaft 4 to rotate the drum 3. Laundry in the drum 3 is lifted up by a baffle 3a so as to fall free due to gravity.
Referring now to FIG. 2, the balance weights 14 and 15, generically represented by a cement 11 element, are fixed to the tub by a locking boss 12 and by a locking bolt 13. Generally, the balance weights 14 and 15 are made of either cement or cast-iron. A process of making a cement balance weight follows.
First, a mold having a predetermined shape is disassembled. Cement is then injected into the disassembled mold. Then, the mold is reassembled and the cement is cured by thermal treatment. The mold is then disassembled and the cured and molded cement is removed. The surface of the molded cement is then trimmed and treated with a spray coating. The completed balance weights 14 and 15 are then located on the locking boss 12 and the locking bolt 13 is mated with the locking boss 12 to complete the assembly.
While generally successful, the above process of preparing the balance weights 14 and 15 and fixing them to the tub 2 has problems. For example, the overall process is rather complicated, has low productivity, and is relatively costly. Moreover, cement balance weights 14 and 15 formed and mounted as described suffer from problems related to the locking boss 12 and locking bolt 13 being directly coupled with the cement 11 (which generically represents the balance weights 14 and 15). Relative motion between the cement balance weights 14 and 15 and the locking structure generates dust. Thus, the working environment is degraded and the cement dust can negatively impacts worker's health.
In contrast to cement weights, cast-iron balance weights require painting to prevent rust, a boring process for forming a locking hole, and a subsequent step of removing metal burrs. Thus, cast-iron balance weights have their own set of fabrication problems. Moreover, cast-iron balance weights 14 and 15 are vulnerable to vibration that unscrews the locking bolt 13.
Therefore, a new cement balance weight would be beneficial. Even more beneficial would be a new cement balance weight that is easier and less costly to fabricate. Still more beneficial would be a new cement balance weight that does not produce cement dust.